A power converter, e.g., a direct current (DC) to DC converter, is utilized in many electrical circuit applications, e.g., a Light Emitting Diode (LED) driver circuit. A DC-DC converter includes a hysteretic comparator with a reference voltage as one of its inputs. A controlled voltage of the converter is compared to hysteretic levels, and a high-side switch is turned on if the controlled voltage level is lower than a low threshold point while a low-side switch is turned on if the controlled voltage level is higher than a high threshold point.
However, a conventional DC-DC converter suffers an output offset problem that causes an output current inaccuracy, because of the response time of the hysteretic comparator and/or a loop delay. In an integrated circuit, the current inaccuracy problem becomes worse over process, voltage, and temperature (PVT) variations. For example, the controlled voltage of the converter is supposed to have an average level between two hysteretic threshold points, assuming that the high-side or low-side switch activates immediately when the controlled voltage level crosses a corresponding threshold point.
In a real comparator circuit, there is a response time for the switching action, which causes equivalent threshold levels to deviate. The deviation levels depend on the slew-rate rate of inputs to the comparator as well as PVT. The overall loop delay from output of the comparator corresponding to respective high/low side switching also causes the threshold levels vary with PVT variations. The threshold variation causes inaccuracy of controlled voltage and current.